1. Field of the Invention
The present invention relates to a silent-chain transmission apparatus which uses a silent chain including plates capable of reducing noise generated from meshing engagement between the silent chain and a sprocket.
2. Description of the Related Art
In conventional silent-chain transmission apparatuses for used in engines, etc., various kinds of improved chain plates are use in order to reduce noise generated during operation. However, the noise-reducing performances of these plates are considered unsatisfactory.
For example, the conventional silent-chain transmission apparatus disclosed in Japanese Patent Publication (kokoku) No. 1-56304 uses a silent chain as shown in FIG. 6A. In the silent chain, outer flanks 2A of a pair of teeth of one plate 1A are formed such that they project outward from inner crotches 3B of teeth of another plate 1B that overlaps with and is offset from the plate 1A by a single tooth pitch. The silent chain exhibits a so-called "outer-flank contact" process as shown in FIG. 6B, in which at the point where the silent chain starts to engage the sprocket S, an outer flank 2B of one plate 1A located at the rear side in the travel direction first comes into contact with a tooth of the sprocket S, and at the point where the silent chain establishes complete engagement with the sprocket S, both outer flanks 2C of an adjacent plate 1C come into contact with other teeth of the sprocket S.
In such a silent-chain transmission apparatus, since only the outer flanks of each plate come into contact with teeth of the sprocket S, a large impact force acts on the outer flanks, resulting in rapid wear of the outer flanks and generation of harsh noise.
Meanwhile, the conventional silent-chain transmission apparatus disclosed in Japanese Patent Publication (kokoku) No. 1-56304 uses another silent chain as shown in FIG. 7A. In the silent chain, inner crotches 3A of a pair of teeth of one plate 1A are formed such that they project outward from outer flanks 2B of teeth of another plate 1B that overlaps with and is offset from the plate 1A by a single tooth pitch. The silent chain exhibits a so-called "inner-crotch/outer-flank two-step contact" process as shown in FIG. 7B, in which at the point where the silent chain starts to engage the sprocket S, an outer flank 2B of one plate 1B and an inner crotch 3A of another plate 1A that overlaps with the plate 1B come into contact with the same tooth of the sprocket S at the same time or with a time difference therebetween.
In such a silent-chain transmission apparatus, meshing engagement is established in the vicinity of a working pitch line L, and the load tension of the chain acting on the teeth concentrates at the vicinity of the working pitch line L. Therefore, the tooth surface of the sprocket S wears easily and such wear cannot be avoided.
Further, the conventional silent-chain transmission apparatus disclosed in Japanese Patent Application Laid-Open (kokai) No. 10-2383 uses a silent chain as shown in FIG. 8. In the silent chain, projections 3A', 3B', and 3C' each having a curved profile are formed at the tip portions of inner crotches 3A, 3B, and 3C of plates 1A, 1B, and 1C, which constitute the silent chain. The silent chain exhibits a so-called "inner-crotch/outer-flank two-step contact" process, in which at the point where the silent chain starts to engage the sprocket S, the projection 3A' of, for example, the inner crotch 3A come into contact with a tooth of the sprocket S, and the outer flank 2B then comes into contact with the same tooth of the sprocket S.
In such a silent-chain transmission apparatus, the projections come into contact with teeth of the sprocket S at positions offset toward the teeth tips with respect to the working pitch line L, while the outer flanks 2A, 2B, and 2C come into contact with and seat on the teeth at positions on the working pitch line L. Therefore, the load tension of the chain acting on the teeth does not concentrate at the vicinity of the working pitch line L, and thus the problem involved in the silent-chain transmission apparatus shown in FIGS. 6A and 6B has been solved. However, since the projections have a curved profile and therefore come into sliding contact with teeth of the sprocket through the same portions, the projections of the inner crotches wear easily, so that the endurance strength of the entire chain cannot be maintained for a long period of time.